Low pressure hydrogen discharges

Abstract

This article presents a fluid-plasma model of the free-fall regime of maintenance of high-frequency discharges in hydrogen. The obtained results are for the radial profiles of the concentrations and the velocities of electrons, positive H+, H2+, and H3+ ions, negative H− ions, potential of the radial dc electric field, and electron temperature. The importance of the directed motion of the charged particles in the radial dc electric field, the negative ion behavior in the discharge, and the description of the discharge characteristics by continuous radial profiles, which smoothly cover the total cross section of discharge, are stresses. A strong impact of the negative ions on the formation of the self-consistent discharge structure is shown. The discussions are in terms of changing gas pressure and electron concentration at the discharge axis.

Semi-analytical modeling of the NIO1 source

“…The results shows that the temperature decreases with increasing pressure, whereas the electron density increases; The T e decrease with increasing pressure is due the particle conservation in the continuity equation, in which ν iz ∝ p gas T A e exp(−B/T e ) (the ionization frequency depends linearly on the gas pressure and with the Arrhenius' equation on the electron temperature). This trend well agrees with other numerical simulations for a hydrogen discharge [14], which take into account the Debye sheath and all the ionic (H + , H + 2 , H + 3 , H − ) and neutral H and H 2 species. At higher pressures both the temperature and density profiles become steeper, in particular their peak is under the coil (where there is the main power deposition).…”

“…At first, to verify the correct implementation in COMSOL we modeled the simple case of a plasma with uniform power density deposition and in high pressure regime (D a = D a0 ), for which an analytical solution is possible. In fact, assuming a uniform p abs and T e (even if it is not generally true, since the temperature is expected to be higher in the coil region this is a valid approximation [14]) the continuity equation becomes linear:…”

Negative hydrogen ion maintenance in small radius discharges: Two-dimensional modeling

“…Based on the results from the 1D models of such a discharge 25,26 showing high concentration of the negative ions when the discharge radius is small ͑R =2-3 cm͒, the radius of the discharge is fixed at R = 2.25 cm ͑Fig. 1͒.…”

“…On the other hand, recent one-dimensional ͑1D͒ models 25,26 of hydrogen discharges reveal the presence of high concentration of negative ions at the discharge axis in a single-chamber rf driven source, and the lower the radius, the stronger the effect is, with an optimum at radii of 2-3 cm. The reason for this accumulation of the ions in the on-axis region of the discharge is in the flux-in the radial dc electric field-of the negative ions produced all over the discharge cross section and in the possibility for the ions to reachwithout being destroyed in collisions-the discharge center, which is only possible when the discharge radius is small.…”

“…This study is an extension of the previous 1D models 25,26 toward 2D modeling of small radius hydrogen discharges. At the current stage, diffusion-controlled discharges are considered.…”